Catalyst and method for the production of polytetrahydrofuran

ABSTRACT

Polytetrahydrofuran, polytetrahydrofuran copolymers, diesters or monoesters of these polymers are prepared by polymerization of tetrahydrofuran in the presence of at least one telogen and/or comonomer, which is in the form of shaped catalyst bodies or catalyst particles having a volume of the individual shape of the body or particle of at least 0.05 mm 3 , preferably at least 0.2 mm 3 , in particular 1 mm 3 , and has at least one of the features a) and b):
     a) a pore radius distribution having at least one maximum in the pore radius range from 100 to 5000 Å,   b) a pore volume of catalyst pores having radii of 200–3000 Å of greater than 0.05 cm 3 /g and/or a pore volume of pores having radii of 200–5000 Å of greater than 0.075 cm 3 /g and/or a pore volume of pores having radii of &gt;200 Å of greater than 0.1 cm 3 /g.

The present invention relates to a catalyst for preparingpolytetrahydrofuran, polytetrahydrofuran copolymers, diesters ormonoesters of these polymers by polymerization of tetrahydrofuran in thepresence of at least one telogen and/or comonomer.

Polytetrahydrofuran (hereinafter referred to as “PTHF”), which is alsoknown as polyoxybutylene glycol, is a versatile intermediate in theplastics and synthetic fibers industries and is employed, inter alia, asa diol component for producing polyurethane, polyester and polyamideelastomers. In addition, it is, as are some of its derivatives, avaluable auxiliary in a variety of applications, e.g. as a dispersant orin the deinking of waste paper.

In industry, PTHF is usually prepared by polymerization oftetrahydrofuran (hereinafter referred to as “THF”) over suitablecatalysts in the presence of reagents whose addition makes it possibleto control the chain length of the polymer chains and thus to set themean molecular weight (chain termination reagents or “telogens”). Thechain length is controlled via selection of type and amount of telogen.The choice of suitable telogens additionally makes it possible tointroduce functional groups at one end or at both ends of the polymerchain.

Thus, for example, the use of carboxylic acids or carboxylic anhydridesas telogens makes it possible to prepare monoesters or diesters of PTHF.PTHF itself is only formed by subsequent saponification ortransesterification. This preparation is therefore referred to as atwo-stage PTHF process.

Other telogens act not only as chain termination reagents but are alsoincorporated into the growing polymer chain of PTHF. They not only havethe function of a telogen but are at the same time a comonomer and cantherefore be referred to as telogens and as comonomers with equaljustification. Examples of such comonomers are telogens having twohydroxy groups, for example diols (dialcohols). These can be, forexample, ethylene glycol, propylene glycol, butylene glycol,1,3-propanediol, 1,4-butanediol, 2-butyne-1,4-diol, 1,6-hexanediol orlow molecular weight PTHF. Further suitable comonomers are cyclic etherssuch as 1,2-alkylene oxides, e.g. ethylene oxide or propylene oxide,2-methyltetrahydrofuran and 3-methyltetrahydrofuran. The use of suchcomonomers leads, with the exception of water, 1,4-butanediol and lowmolecular weight PTHF, to the formation of tetrahydrofuran copolymers,hereinafter referred to as THF copolymers, and in this way makes itpossible to chemically modify PTHF.

Industrially, PTHF can be prepared in a single stage by polymerizationof THF using water, 1,4-butanediol or low molecular weight PTHF astelogen over acid catalysts. Known catalysts include both homogeneoussystems dissolved in the reaction system and heterogeneous, i.e. largelyundissolved, systems. However, the relatively low THF conversions whichare, in particular, achieved in the synthesis of PTHF having a molecularweight of from 650 to 3000 represent a disadvantage.

On a large industrial scale, processes employed are predominantly theabovementioned two-stage processes in which THF is firstly polymerized,e.g. in the presence of fluorosulfonic acid, to form polytetrahydrofuranesters and these are subsequently hydrolyzed to PTHF. This form of THFpolymerization usually achieves higher THF conversions than dosingle-stage processes. A particularly advantageous method ispolymerization of THF in the presence of carboxylic anhydrides orcarboxylic anhydride/carboxylic acid mixtures, e.g. acetic anhydride oracetic anhydride/acetic acid mixtures, and in the presence of acidcatalysts to form PTHF acetates and subsequent transesterification ofthe PTHF acetates with, for example, methanol to form PTHF and methylacetate.

The preparation of PTHF by polymerization of THF in the presence ofcarboxylic anhydrides and/or carboxylic anhydride/carboxylic acidmixtures and the preparation of THF copolymers by polymerization of THFin the presence of carboxylic anhydrides and/or carboxylicanhydride/carboxylic acid mixtures and cyclic ethers as comonomers oversolid acid catalysts, which are preferred for the purposes of thepresent patent application, are known.

DE-A-198 01 462 describes acid-activated calcium montmorillonites havinga specific surface area of >300 m²/g, an acidity of >0.02 mmol/g forpK_(a) values of <−3 and pore volumes of >0.4 cm³/g for pore sizes inthe range 30 to 200 Å as catalysts in powder or extrudate form for thepolymerization of THF to form, inter alia, PTHF diacetates.

U.S. Pat. No. 4,228,462 describes a method of preparing copolymers ofTHF and alkylene oxides over acid-activated montmorillonites having porevolumes of 0.4 to 0.8 cm³/g, average pore sizes in the range 0.1 to 0.3μm and a surface area of 220 to 260 m²/g. A continuous preparation insuspension with the catalyst being used in powder form is described.

According to DE-C2-195 13 493, calcined magnesium-aluminumhydrosilicates of the attapulgite or sepiolite type are used as catalystfor preparing polytetramethylene ether glycol diesters. The use of thesecatalysts instead of the known montmorillonite, zeolite or kaolincatalysts is said to lead to higher polymerization rates and moreuniform properties and a more uniform molecular weight distribution ofthe polymers obtained.

JP-A-11-292958 describes a process for the continuous preparation ofPTHF diesters having an improved molecular weight distribution. Theprocess is carried out over a solid inorganic acid catalyst insuspension. Catalysts mentioned are catalysts of the zirconiumoxide/silicon dioxide type or the bleaching earth type, with catalystparticles of <3 mm.

WO-A-94/05719 mentions amorphous aluminum silicates and alsoacid-activated and calcined kaolin or zeolites as catalysts for thepreparation of PTHF esters of dicarboxylic acids having a narrowmolecular weight distribution by polymerization of THF in a fixed bed inthe presence of carboxylic anhydrides.

The abovementioned processes show that the polymerization catalystsbased on sheet silicates which are used do display a high catalystactivity in powder form, i.e. in a suspension process. On the otherhand, in the case of the preferred method of production in a fluidizedbed or fixed bed, which offers advantages in separation from thecatalyst compared to the suspension mode, the catalysts describeddisplay a greatly reduced activity when used as shaped bodies. However,the economics of a heterogeneously catalyzed PTHF process are criticallydependent on the productivity of the catalyst.

It is an object of the present invention to provide a catalyst for thepreparation of polytetrahydrofuran, polytetrahydrofuran copolymers,diesters or monoesters of these polymers which is easy to separate offand at the same time displays a high productivity, especially when usedin a fluidized bed or fixed bed.

We have found that this object is achieved by a catalyst which is in theform of shaped bodies or particles having a volume of at least 0.05 mm³,preferably at least 0.2 mm³ and particularly preferably at least 1 mm³.Furthermore, the catalyst has at least one of the features a) and b):

-   a) A pore radius distribution which displays at least one maximum in    the pore radius range from 100 to 5000 Å;-   b) A pore volume of catalyst pores having radii of from 200 to 3000    Å of greater than 0.05 cm³/g, preferably greater than 0.075 cm³/g    and/or a pore volume of catalyst pores having radii of from 200 to    5000 Å of greater than 0.075 cm³/g, preferably greater than 0.1    cm³/g and/or a pore volume of catalyst pores having a radius of >200    Å of greater than 0.1 cm³/g, preferably greater than 0.15 cm³/g.

Preference is given to catalysts which have both the features a) and b).

A volume of the individual shaped catalyst body or catalyst particle ofat least 0.05 mm³ advantageously makes it possible for the catalyst tobe easily separated off from the polymer, e.g. by decantation and/orfiltration in the case of a suspension process or when used in afluidized bed or fixed bed.

In a further preferred embodiment, 50% of the total pore volume is madeup by pores having a diameter of <0.1 μm.

The production of shaped catalyst bodies from pulverulent raw materialscan be carried out by methods known to those skilled in the art, forexample tabletting, agglomeration or extrusion, as are described, forexample, in the Handbook of Heterogeneous Catalysis, Vol. 1, VCHVerlagsgesellschaft Weinheim, 1997, pp. 414–417. Auxiliaries known tothose skilled in the art, for example binders, lubricants and/orsolvents, can be added during the shaping step. Preference is given toshaping by agglomeration or extrusion in the presence of water asauxiliary.

As raw materials for the novel shaped catalyst bodies having theabovementioned pore structure, it is possible to use pulverulentcatalysts which initiate the polymerization of THF in the presence ofcarboxylic anhydrides or carboxylic anhydride/carboxylic acid mixturesand/or cyclic ethers. Preference is given to catalyst raw materialswhich display a satisfactory initial productivity when used in powderform in a standardized polymerization test. For the purposes of thepresent invention, initial productivity means the productivity of thecatalyst at negligibly low THF conversions, as can be determined, forexample, from a batchwise polymerization experiment as described in theexamples. This initial productivity of the catalyst raw material inpowder form is at least 0.5 g of PTHF or PTHF derivative per g ofcatalyst powder and hour of reaction time; preference is given to rawmaterials having an initial productivity of at least 1 g/g*h,particularly preferably at least 2.5 g/g*h.

The shaped catalyst bodies of the present invention are not restrictedto catalysts which are produced by shaping of active compositions. Theprocess of the present invention can likewise be carried out usingcatalysts produced by converting a shaped body having little or nopolymerization activity into a catalyst according to the presentinvention by further treatment. Examples of such catalysts are bleachingearths activated as shaped bodies or mixed oxide catalysts obtained byimpregnation or coating of support materials. In this embodiment, thecatalysts of the present invention likewise have a powder activity of atleast 0.5 g of PTHF or PTHF derivative per g of catalyst powder and hourof reaction time, preferably 1 g/g*h and particularly preferably 2.5g/g*h. The measurement of this initial activity can be carried out, forexample, on a sample obtained by milling the shaped body to obtain apowder or by measurement on a chemophysically analogous material inpowder form.

As active catalyst composition, use is made of acidic solids known tothose skilled in the art. According to the present invention, the use ofsheet silicates is preferred. Preferred sheet silicates are those of themontmorillonite/saponite group, kaolin/serpentine group or thepalygorskite/sepiolite group, particularly preferably montmorillonites,hectorites, kaolins, attapulgites or sepiolites, as are described, forexample, in Klockmanns Lehrbuch der Mineralogie, 16^(th) Edition, F.Euke Verlag 1978, pages 739–765.

Before use in the process of the present invention, the sheet silicatecatalysts are preferably activated in acid. The activation can becarried out by methods whose principles are described, for example, inU.S. Pat. No. 1,642,871 or the references cited in EP-A-0 398 636. Theacid activation can be carried out by means of various acids, preferablycustomary mineral acids or organic carboxylic acids. The acids arepreferably selected from the group consisting of hydrochloric acid,sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acidand citric acid. Particular preference is given to sulfuric acid and/orhydrochloric acid.

To carry out the acid activation, it is possible, for example, tosuspend the sheet silicate in powder form in acid and to react andactivate it under known conditions. This gives an active catalyst rawmaterial in powder form. To remove adhering traces of acid, it cansubsequently be washed with distilled or deionized water and then driedor calcined. The drying of the sheet silicate catalysts isadvantageously carried out at atmospheric pressure and temperatures offrom 80 to 200° C., preferably from 100 to 150° C., for from 1 to 20hours. Drying can also be carried out under reduced pressure and atlower temperatures.

However, the acid activation can also be carried out in other ways whichare known per se. For example, the acid can be brought into contact withthe sheet silicate by spraying or kneading with simultaneous shaping, asdisclosed, for example, in WO-A-99/39820.

Calcination of the catalysts is preferably carried out at from 150 to900° C., particularly preferably from 200 to 700° C., in particular from300 to 500° C., for from 0.1 to 12 hours, preferably from 1 to 5 hours.Both pulverulent catalyst raw materials and preferred shaped catalystbodies can be calcined.

The catalyst porosity specified according to the present invention isachieved by methods known to those skilled in the art. These are, forexample, addition of pore formers (carboxylic acids, nitrates, ammoniumsalts, guanidinium salts, urotropin, proteins, carbohydrates or modifiedcarbohydrates such as methylcellulose), inorganic additives (metaloxides, clay minerals) as mentioned in, for example, DE-A-196 01 861,choice of an appropriate particle size distribution of the catalystpowder, pretreatment of the catalyst powder, e.g. precalcination ormilling of precalcined shaped bodies, and/or appropriate processparameters in the production of the shaped body, for example limitedcompaction of the powder in the shaping step.

As pore formers and auxiliaries and/or additives, preference is given tothose in which only a low level of soluble alkaline metals and otherconstituents which adversely affect the catalytic activity is presentand/or is formed during heat treatment and/or under the reactionconditions. Particularly preferred additives from this category areammonium nitrate, silicon dioxides, aluminum oxides and clay minerals.The porosity can be set both in the production of the shaped catalystbodies from active compositions and in the production of shaped bodieshaving little or no activity which are subsequently subjected toactivation.

The catalysts which can be used according to the present invention canbe employed for the polymerization in the form of, for example,cylinders, extrudates, ribbed extrudates, spheres, rings or granules.

Possible pretreatments of the catalyst are, for example, drying by meansof gases such as air or nitrogen which have been heated to 80–200° C.,preferably to 100–150° C.

Telogens suitable for the preparation of PTHF esters are carboxylicanhydrides and/or carboxylic anhydride/protic acid mixtures. The proticacids are preferably organic and inorganic acids which are soluble inthe reaction system. Examples of organic acids are carboxylic acids andsulfonic acids. Examples of inorganic acids are sulfuric acid,hydrochloric acid, phosphoric acid.

Preference is given to using organic carboxylic acids or theiranhydrides. Among these, preference is given to aliphatic and aromaticpolycarboxylic and/or monocarboxylic acids containing from 2 to 12,preferably from 1 to 8, carbon atoms. Preferred examples of aliphaticcarboxylic acids are acetic acid, lactic acid, propionic acid, valericacid, caproic acid, caprylic acid and pelargonic acid. Examples ofaromatic carboxylic acids are phthalic acid and naphthalenecarboxylicacid. Examples of anhydrides of aliphatic polycarboxylic acids aresuccinic and maleic anhydride. Particular preference is given to aceticanhydride.

The PTHF acetates formed when using the preferred telogens can beconverted into PTHF by various methods (e.g. as described in U.S. Pat.No. 4,460,796).

Other copolymers of THF can be prepared by the additional use of cyclicethers which can be polymerized with opening of the ring, preferably athree-, four- or five-membered ring, for example 1,2-alkylene oxides,e.g. ethylene oxide or propylene oxide, oxetane, substituted oxetanessuch as 3,3-dimethyloxetane, the THF derivatives 2-methyltetrahydrofuranand 3-methyltetrahydrofuran, as comonomers, with particular preferencebeing given to 2-methyltetrahydrofuran or 3-methyltetrahydrofuran.

The telogen and, if desired, the comonomer are advantageously introducedinto the polymerization as solutions in THF. Since the telogen leads tochain termination or chain transfer in the polymerization, the meanmolecular weight of the polymer can be controlled via the amount oftelogen used. The more telogen present in the reaction mixture, thelower the mean molecular weight of the PTHF or PTHF derivative obtained.Depending on the telogen content of the polymerization mixture, it ispossible to prepare PTHF, the relevant PTHF derivatives or THFcopolymers having mean molecular weights of from 250 to 10000 dalton ina targeted manner. The process of the present invention is preferablyused to prepare PTHF, the relevant PTHF derivatives or THF copolymershaving mean molecular weights of from 500 to 5000 dalton, particularlypreferably from 650 to 4000 dalton.

The polymerization is generally carried out at from 0 to 80° C.,preferably from 25° C. to the boiling point of THF. The pressureemployed is generally not critical for the result of the polymerization,and the polymerization is therefore generally carried out at atmosphericpressure or under the autogenous pressure of the polymerization system.Exceptions are copolymerizations of THF with volatile 1,2-alkyleneoxides, which are advantageously carried out under superatmosphericpressure. The pressure is usually from 0.1 to 20 bar, preferably from0.5 to 2 bar.

To avoid the formation of ether peroxides, the polymerization isadvantageously carried out under an inert gas atmosphere. Inert gaseswhich can be used are, for example, nitrogen, carbon dioxide or noblegases; preference is given to using nitrogen.

The polymerization is particularly advantageously carried out under ahydrogen atmosphere. This embodiment results in a particularly low colornumber of the polymers formed. The hydrogen partial pressure can bechosen in the range from 0.1 to 50 bar. When carrying out thepolymerization in the presence of hydrogen, the color number can beimproved further by doping the polymerization catalyst with transitionmetals or mixing the polymerization catalyst with a catalyst comprisingtransition metal(s). Suitable transition metals are the elements ofgroups 7 to 10 of the Periodic Table, for example ruthenium, rhenium,nickel, iron, cobalt, palladium and/or platinum.

The process of the present invention can be carried out batchwise orcontinuously. For economic reasons, continuous operation is generallypreferred.

When the process is carried out batchwise, the reactants THF, therelevant telogen and/or, if desired, the comonomer and the catalyst aregenerally reacted in a stirred vessel or loop reactor at thetemperatures indicated until the desired conversion of THF has beenreached. The reaction time can be from 0.5 to 40 hours, preferably from1 to 30 hours, depending on the amount of catalyst added. The catalystsare generally added to the polymerization mixture in an amount of from 1to 90% by weight, preferably from 4 to 70% by weight and particularlypreferably from 8 to 60% by weight, based on the weight of the THF used.

In the case of a continuous process, a reaction can be carried out inthe suspension mode or the fixed-bed mode in conventional reactors orreactor assemblies suitable for continuous processes, in the case of thesuspension mode in, for example, loop reactors or stirred reactors andin the case of the fixed-bed mode in tube reactors or fixed-bedreactors. The fixed-bed mode is preferred.

In the preferred fixed-bed mode, the polymerization reactor can beoperated in the upflow mode, i.e. the reaction mixture is conveyed fromthe bottom upward, or in the downflow mode, i.e. the reaction mixture ispassed through the reactor from the top downward. The feed comprisingTHF and telogen and/or comonomer is fed continuously to thepolymerization reactor, with the WHSV over the catalyst being from 0.01to 2.0 kg of THF/(1*h), preferably from 0.02 to 1.0 kg of THF/(1*h) andparticularly preferably from 0.04 to 0.5 kg of THF/(1*h).

Furthermore, the polymerization reactor can be carried out in a singlepass, i.e. without recirculation of product, or in the circulation mode,i.e. part of the polymerization mixture leaving the reactor isrecirculated. In the recirculation mode, the ratio of recirculatedreaction mixture to fresh feed is less than or equal to 100:1,preferably less than 80:1 and preferably less than 60:1.

The concentration of the carboxylic anhyride used as telogen in the feedfed to the polymerization reactor is from 0.03 to 30 mol %, preferablyfrom 0.05 to 20 mol %, particularly preferably from 0.1 to 10 mol %,based on the THF used.

If a carboxylic acid is used in addition, the molar ratio of this tocarboxylic anhydride in the feed is usually from 1:20 to 1:20000.

If comonomers are used in addition, the molar ratio of these to THF inthe feed is usually from 0.1 to 50 mol %, preferably from 0.5 to 40 mol%, particularly preferably from 1 to 30 mol %.

If the polymerization has been carried out by a suspension process,work-up of the polymerization product is carried out by separating offthe major part of the polymerization catalyst from the polymerizationmixture, for example by filtration, decantation or centrifugation, andpassing the polymerization product obtained to further work-up. In thepreferred fixed-bed mode, the polymerization product is directly workedup further.

The work-up of the particularly preferred PTHF acetates or THF copolymeracetates can be carried out by methods known per se. For example,unreacted THF and any acetic anhydride, acetic acid and comonomer arefirstly separated off by distillation and the resulting PTHF acetate orTHF copolymer acetate is transesterified with methanol in the presenceof a basic catalyst to form PTHF or THF copolymer and methyl acetate.

If desired, low molecular weight PTHF and/or tetrahydrofuran copolymerhaving a mean molecular weight of from 200 to 700 dalton cansubsequently be separated off by distillation. Low molecular weightcyclic oligomers can usually also be separated off by distillation inthis way. The distillation residue which remains consists of PTHF or THFcopolymer having a mean molecular weight of from 650 to 10000 dalton.

After use in a batchwise or continuous PTHF process, the catalysts ofthe present invention can be regenerated, for example by heat treatmentas described in EP-A-0 535 515 and/or by washing the catalyst withaqueous and/or organic solvents.

The invention is illustrated by the examples below.

I. Analytical Examination of the Catalysts

The porosity and pore volume distribution of the catalysts weredetermined by mercury intrusion in accordance with DIN 66133. The datawere evaluated in the pore radius range from 20 Å to 10 μm. Reportedmaxima in the pore radius distribution are based on a logarithmic plotof the pore radius.

II. Determination of the Initial Activity of the Catalyst in Powder Form

200 g of tetrahydrofuran and 20 g of acetic anhydride are placed in a250 ml flask and heated to 50° C. While stirring vigorously, 5 g offinely powdered catalyst which has been dried at 120° C. and has aparticle size of <100 μm is added and vigorous stirring of the reactionmixture is continued at 50° C. 20 ml samples of the reaction mixture aretaken after 45 minutes, 2 h, 4 h and 6 h and are in each caseimmediately separated from the catalyst powder by filtration. Thesamples which have been freed of the catalyst are analyzed to determinetheir PTHF diacetate content, e.g. by distillating off the low boilersand weighing the PTHF diacetate. The initial productivity of thecatalyst powder is determined by extrapolation of the plot of PTHFdiacetate formation versus time.

III. Determination of the Activity of Shaped Catalyst Bodies

A 120 ml tube reactor provided with a double wall for temperaturecontrol and a recirculation loop was charged with 100 ml of dried shapedcatalyst bodies which had previously been dried at 150° C. for 24 hours.A mixture of 200 g of tetrahydrofuran and 20 g of acetic anhydride wassubsequently pumped at 50° C. (measured in the circulated thermostatedliquid for the double wall) under protective gas through the catalystbed at a circulation rate of 1 l/h. Samples were taken from the reactionmixture after 15, 30, 45, 60, 90 and 120 minutes and analyzed for theirpolymer content (see under II.). The initial productivity of the shapedcatalyst bodies was determined by extrapolation of the plot of PTHFdiacetate formation versus time.

The above-described examples of the determination of the activity caneasily be adapted in respect of type and amount of telogens and/orcomonomers, temperature, pressure, etc., to the respective useconditions of the catalyst. Furthermore, variation of amounts ofcatalyst and reaction times enables the process to be easily adapted tovarious initial activities.

EXAMPLE A Comparative Catalyst

350 g of an acid-activated sheet silicate (bleaching earth K10, fromSüdchemie) having a powder activity of 7.8 g/g*h was intensively kneadedwith 225 ml of water in a laboratory kneader for 2.5 hours, subsequentlyextruded to give extrudates having a diameter of 2.5 mm and a meanlength of 10 mm, dried and calcined at 350° C. The pore radiusdistribution (Hg porosimetry) of this catalyst displays no discerniblemaximum in the pore radius range >20 Å, and the porosity in the poreradius range from 200 Å to 3000 Å is 0.035 cm³/g. The activity of theshaped bodies of this comparative catalyst serves as reference for theother catalysts.

EXAMPLE B Catalyst 1 According to the Present Invention

350 g of an acid-activated sheet silicate (bleaching earth K10, fromSüdchemie) having a powder activity of 7.8 g/g*h was intensively kneadedwith 260 ml of water in a laboratory kneader for 26 minutes,subsequently extruded to give extrudates having a diameter of 2.5 mm anda mean length of 10 mm, dried and calcined at 350° C. The pore radiusdistribution (Hg porosimetry) of this catalyst is bimodal with maxima atpore radii of 60 Å and 1000 Å, and the porosity in the pore radius rangefrom 200 Å to 3000 Å is 0.15 cm³/g. The activity of the shaped bodies ofthis catalyst is about 2.9 times that of the comparative catalyst fromExample A.

Catalyst 2 According to the Present Invention

387 g of an acid-activated sheet silicate (bleaching earth K10, fromSüdchemie) having a powder activity of 7.8 g/g*h were firstlyprecalcined at 300° C., then intensively kneaded with 300 ml of water ina laboratory kneader for 25 minutes, subsequently extruded to formextrudates having a diameter of 2.5 mm and a mean length of 10 mm, driedand subsequently calcined at 350° C. The pore radius distribution (Hgporosimetry) of this catalyst is bimodal with a weak maximum in therange from 20 to 100 Å and a distinct maximum at 3000 Å. The porosity inthe pore radius range from 200 to 3000 Å is 0.32 cm³/g. The activity ofthe shaped bodies of this catalyst is about 4.9 times that of thecomparative catalyst from Example A.

IV. Continuous Polymerization of THF to Give PTHF Diacetate

EXAMPLE C Comparative Catalyst

In a laboratory apparatus, a mixture of THF and acetic anhydride (6.9%based on the total feed) was passed at 45° C. under protective gas overthe comparative catalyst from example A which had been predried at 140°C. and was installed as a fixed bed in a 250 ml reactor (internaldiameter: 40 mm). The WHSV over the catalyst was 0.2 kg of feed/(l ofcat.*h). The reactor was operated with product recirculation (1 l/h). Towork up the PTHF diacetate, the reaction mixture obtained was freed ofunreacted THF and acetic anhydride by distillation. The loss ondistillation was 36%, and the molecular weight M_(n) of the PTHFdiacetate was 760 g/mol.

EXAMPLE D Catalyst 3 According to the Present Invention

300 g of an acid-activated sheet silicate (bleaching earth K10, fromSüdchemie) having a powder activity of 5.4 g/g*h were firstlyprecalcined at 300° C., then intensively kneaded with 190 ml of water ina laboratory kneader for 25 minutes, subsequently extruded to formextrudates having a diameter of 2.5 mm and a mean length of 10 mm, driedand subsequently calcined at 350° C. The pore radius distribution (Hgporosimetry) of this catalyst is bimodal with a weak maximum in therange from 20 to 100 Å and a distinct maximum at 3000 Å. The porosity inthe pore radius range from 200 to 3000 Å is 0.27 cm³/g.

In a laboratory apparatus, a mixture of THF and acetic anhydride (6.9%based on the total feed) was passed at 45° C. under protective gas overthis catalyst which had been predried at 140° C. and was installed as afixed bed in a 250 ml reactor (internal diameter: 40 mm). The WHSV overthe catalyst was 0.2 kg of feed/(l of cat.*h). The reactor was operatedwith product recirculation (1 l/h). To work up the PTHF diacetate, thereaction mixture obtained was freed of unreacted THF and aceticanhydride by distillation. The loss on distillation was 51%, and themolecular weight M_(n) of the PTHF diacetate was 960 g/mol.

1. A catalyst for the preparation of polytetrahydrofuran,polytetrahydrofuran copolymers, diesters or monoesters of these polymersby polymerization of tetrahydrofuran in the presence of at least onetelogen and/or comonomer, which is in the form of shaped catalyst bodiesor catalyst particles having a volume of the individual shape of thebody or particle of at least 0.05 mm³ and has both of the features a)and b): a) a pore radius distribution having at least one maximum in thepore radius range from 100 to 5000 Å, b) a pore volume of catalyst poreshaving radii of 200 to 3000 Å of greater than 0.05 cm³/g and/or a porevolume of pores having radii of 200 to 5000 Å of greater than 0.075cm³/g and/or a pore volume of pores having radii >200 Å of greater than0.1 cm³/g, and wherein the active catalyst composition is selected fromamong sheet silicates.
 2. A catalyst as claimed in claim 1, wherein 50%of the total pore volume is made up by pores having a diameter of >0.1μm.
 3. A catalyst as clauned in claim 1 which is produced from acatalyst precursor in powder form.
 4. A catalyst as claimed in claim 1,wherein the catalyst precursor in powder form or the pulverized catalysthas an initial activity of at least 0.5 g of polymer/g of catalyst andhour of reaction time.
 5. A catalyst as claimed in claim 1, wherein thesheet silicate is selected from the group consisting of themontmorillonite/saponite group the kaolin/serpentine group and thepalygorskite/sepiolite group.
 6. A catalyst as claimed in claim 5,wherein the sheet silicate is selected from among montmorillonite,hectorite, kaolin attapulgite, sepiolite and mixtures thereof.
 7. Aprocess for producing a catalyst as claimed in claim 1, wherein theshaped catalyst bodies are produced from pulverulent raw materialstabletting, agglomeration or extrusion, with auxiliaries, selected fromthe group consisting of binders, lubricants and solvents, being addedduring shaping.
 8. A process as claimed in claim 6, wherein shaping isperformed by agglomeration or extrusion in the presence of water asauxiliary.
 9. A catalyst as claimed in claim 1, wherein the shapedcatalyst bodies or catalyst particles have a volume of 0.2 mm³.
 10. Aprocess for preparing polytetrahydrofuran, polytetrahydrofurancopolymers, diesters or monoesters of these polymers, which comprisespolymerizing tetrahydrofuran in the presence of at least one telogenand/or comonomer and using a catalyst which is in the form of shapedcatalyst bodies catalyst particles having a volume of the individualshape of the body or particle of at least 0.05 mm³, and has both of thefeatures a) and b): a) a pore radius distribution having at least onemaximum in the pore radius range from 100 to 5000 Å. b) a pore volume ofcatalyst pores having radii of 200 to 3000 Å of greater than 0.05 cm³/gand/or a pore volume of pores having radii of 200 to 5000 Å of greaterthan 0.075 cm³/g and/or a pore volume of pores having radii of >200 Å ofgreater than 0.1 cm³/g.
 11. A process as claimed in claim 10 which iscarried out continuously or batchwise.
 12. A process as claim in claim11, which is carried out in a fixed-bed mode.
 13. A process as claimedin claim 10, wherein tetrahydrofuran is polymerized in the presence ofcarboxylic anhydrides to give polytetrahydrofuran or derivatives andcopolymers thereof having molecular weight of from 250 to 10,000.
 14. Aprocess as claimed in claim 13, wherein the carboxylic anhydride isacetic anhydride.
 15. A process as claimed in claim 13, wherein themolecular weight is from 650 to 4,000 dalton.